Efforts are underway to increase the capacity of increasingly scarce frequency allocations to cellular carriers. These efforts have resulted in newer modulation schemes that have higher peak-to-average power ratios (PAPRs) as compared to previous schemes. One such modulation scheme, known as Long Term Evolution (LTE), can have PAPRs in the order of 10 decibels (dB).
Radio frequency (RF) power amplifiers may be inefficient when backed off from their maximum designed power output level unless driven by a switcher, e.g., a direct current (DC)-DC converter. Using a switcher may provide an efficient approach for legacy modulation schemes, e.g., carrier division multiple access (CDMA) and wireless-CDMA (W-CDMA), which have relatively low PAPRs, e.g., approximately 3 dB or less. In these cases, the switcher only has to follow a relatively slowly changing waveform envelope while maintaining sufficient headroom for linearity to provide desired efficiency over a wide range of output power levels.
In LTE, on the other hand, the waveform envelope changes much faster than with the legacy modulation schemes. Traditional switchers may not have the bandwidth to follow these changes in an effective manner.